Switching power converter and active EMI filter circuit thereof

1. A switching power converter comprising: a power stage circuit, including at least one transistor, configured to operably switch an inductor to convert an input power to an output power, the input power including an input current; a switching controller, configured to operably control the at least one transistor; a noise sensing circuit, configured to sense, by sensing an input related signal, a switching noise caused by the switching of the power stage circuit to generate a noise input signal, wherein the input related signal is related to the input current; an AEF (Active EMI Filter) circuit, configured to amplify the noise input signal to generate an amplified noise signal; an injection capacitor, having one end coupled to receive the amplified noise signal and another end to generate a noise cancelling signal, wherein the noise cancelling signal is injected into an input node of the switching power converter, so as to suppress the switching noise and thus reducing EMI, wherein the input power is provided through the input node to the power stage circuit; and a passive filter circuit, wherein the passive filter circuit is coupled between the input node and the power stage circuit, wherein the passive filter circuit includes a filtering inductor and a filtering capacitor for further filtering the switching noise; wherein the noise sensing circuit includes: a sensing resistor, having a first end coupled to the input node and a second end coupled to the power stage circuit, wherein the input related signal corresponds to a voltage across the sensing resistor; a first coupling branch, which includes a first resistor and a first input capacitor coupled in parallel between a first terminal and a second terminal of the first coupling branch, wherein the first terminal of the first coupling branch is directly connected to the first end of the sensing resistor; and a second coupling branch, which includes a second resistor and a second input capacitor coupled in parallel between a first terminal and a second terminal of the second coupling branch, wherein a first terminal of the second coupling branch is directly connected to the second end of the sensing resistor; wherein the noise input signal corresponds to a voltage difference between the second terminal of the first coupling branch and the second terminal of the second coupling branch; wherein the AEF circuit includes: a first amplifier, configured to differentially amplify the noise input signal, wherein the amplified noise signal is generated according to a voltage at an output terminal of the first amplifier; and a second amplifier, wherein the first amplifier amplifies the noise input signal to generate an intermediate signal, wherein the second amplifier receives an AC component of the intermediate signal through a first DC blocking capacitor connected between the first amplifier and the second amplifier and amplifies the AC component of the intermediate signal to generate the amplified noise signal; wherein an AC coupling ratio is higher than a DC coupling ratio of coupling the input related signal for generating the noise input signal through the first and second coupling branches.

2. A switching power converter comprising: a power stage circuit, including at least one transistor, configured to operably switch an inductor to convert an input power to an output power, the input power including an input current; a switching controller, configured to operably control the at least one transistor; a noise sensing circuit, configured to sense, by sensing an input related signal, a switching noise caused by the switching of the power stage circuit to generate a noise input signal, wherein the input related signal is related to the input current; an AEF (Active EMI Filter) circuit, configured to amplify the noise input signal to generate an amplified noise signal; an injection capacitor, having one end coupled to receive the amplified noise signal and another end to generate a noise cancelling signal, wherein the noise cancelling signal is injected into an input node of the switching power converter, so as to suppress the switching noise and thus reducing EMI, wherein the input power is provided through the input node to the power stage circuit; and a passive filter circuit, wherein the passive filter circuit is coupled between the input node and the power stage circuit, wherein the passive filter circuit includes a filtering inductor and a filtering capacitor for further filtering the switching noise; wherein the at least one transistor includes a high side transistor and a low side transistor which are coupled to a switching node for switching one end of the inductor; wherein the input related signal includes a first input related signal and a second input related signal, and the noise input signal includes a first noise input signal and a second noise input signal; wherein the noise sensing circuit includes: a first conversion resistor coupled to sense a current flowing through the high side transistor for generating the first input related signal; a first input capacitor, having one end coupled to receive the first input related signal and another end for generating the first noise input signal at the another end of the first input capacitor; a second conversion resistor coupled to sense a current flowing through the low side transistor for generating the second input related signal; and a second input capacitor, having one end coupled to receive the second input related signal and another end for generating the second noise input signal at the another end of the second input capacitor; wherein the AEF circuit includes: a first amplifier, configured as a non-inverting amplifier for amplifying the first noise input signal to generate a first noise output signal; a second amplifier, configured as an inverting amplifier for amplifying the second noise input signal to generate a second noise output signal; and a third amplifier, configured as a non-inverting adder circuit, wherein a non-inverting input terminal of the third amplifier is coupled to an output terminal of the first amplifier through a first DC blocking capacitor and is also coupled to an output terminal of the second amplifier through a second DC blocking capacitor, such that an AC component of the first noise output signal and an AC component of the second noise output signal are superposed through the third amplifier to generate the amplified noise signal.